We present an approach to scanning tunneling microscopy topographic imaging which pays special attention to the influence of the geometrical shape of the tip and sample. Both electrodes are described by spatially restricted two-dimensional square-well potentials of finite height. Their eigenstates are calculated numerically and their geometry can be chosen arbitrarily. The tunneling current is calculated using the transfer Hamiltonian formalism. We demonstrate the abilities of our approach with the example of constant-current imaging of an idealized nanometer-trench surface-profile structure by different tips.